Inflatable safety belts of this general type are well known, and several varieties are commercially available. Devices of this general type are described by Potts, U.S. Pat. No. 3,181,184; Beaton, U.S. Pat. No. 3,414,920; and Brown, U.S. Pat. No. 5,702,279. The known inflatable PFD's while in the main effective in providing the required level of flotation, suffer from a number of disadvantages. Many of the known PFD's do not sit comfortably on the wearer when uninflated, which leads to the PFD not always being worn when it should be. Effectively all of the known inflatable PFD's are of complex construction, and consequently relatively expensive to make, which again mitigates against the full and proper use of such devices. For example, Brown in U.S. Pat. No. 5,702,279 discloses a two part PFD which is adapted to be worn uninflated around the waist, comprising and inflatable flotation device and a waist belt. When the PFD is inflated, the inflated part separates from the waist part, and is attached thereto by at least one tether. Most of the known PFD's use a single gas cartridge to inflate the PFD, thus exposing the user to risk if the cartridge has leaked, and does not contain sufficient gas.
In order to at least mitigate any difficulties that arise when insufficient gas is available from the cartridge, the known PFD's are often provided with a subsidiary inflation device constructed to be operated orally by the wearer. An oral inflation device can also be used to ensure that the PFD maintains an adequate internal gas pressure over an extended time period after it has been inflated. While these oral inflation devices are effective, they are also subject to one major disadvantage, which is a consequence of the fact that in the deflated condition, prior to use, the PFD is folded up relatively tightly to fit into a cover, for example as shown by Brown in U.S. Pat. No. 5,702,279. Due to this, the access of air into the PFD from an oral inflation device can be either substantially blocked, or even sealed, by the gas inlet nozzle being pressed against the flexible material from which the PFD is made. Any condensation present inside the PFD will have the same effect, and severely hinder inflation.
The fact that the uninflated PFD is folded up relatively tightly can also cause problems even when the gas cartridge is fully charged. The inflatable bladder that provides the required flotation is generally constructed from an elastomer impregnated fabric, such as rubberised nylon. The gas used in the cartridge is generally carbon dioxide. As the carbon dioxide is vented from the cartridge into the PFD expansive cooling occurs, which, as noted by De Boer in U.S. Pat. No. 3,142,850, can result in the formation of both liquid carbon dioxide, and carbon dioxide "snow", thus creating localised temperatures below about -40.degree. C. At this temperature the bladder fabric freezes, loses its flexibility, and cannot be easily separated from the gas inlet nozzle constructions often used. De Boer, in U.S. Pat. No. 3,142,850, recognises this difficulty and describes a gas inlet nozzle which includes a "cold dissipator" adapted to trap carbon dioxide snow. The gas inlet nozzle described by De Boer is intended for inflatable boats and the like, and is relatively large and bulky, thus making it impractical for a personal PFD.
This sealing problem is also exacerbated in many designs, such as Mackal et al, U.S. Pat. No. 3,754,731 and Lind et al, U.S. Pat. No. 5,188,142, by locating the inlet gas nozzle in what is effectively a recess, such as the surrounding upstanding strengthening rim as shown by Mackal et al, or recessed within the end of a threaded fitting, as shown by Lind et al.